The present invention is directed to a T-connector for use in a low-voltage AC service network, and more particularly to a T-connector for use in a service bus manhole or building vault for connecting a bus cable to two tap cables, such as a supply cable and a service cable.
In an electrical power distribution network for use in an urban area, transformers are used to step down high-voltage AC to voltage levels suitable for use in buildings. The reduced-voltage power is then distributed via a low voltage AC service network. The term "low-voltage" in the electrical power industry means 600 volts or below.
The particular configuration of the low-voltage AC service network may vary depending upon a number of factors, such as the power requirements of the customers, local regulation, and the date when the network was initially installed. Typically a multi-cable bus in a manhole is connected to three-phase stepdown transformers by supply cables. The cables of the bus are in turn connected by service cables to metering cabinets in the building or buildings served by the network. Limiters placed into the supply and service cables serve as fuses to provide protection in the event of accidental short-circuits or unexpectedly high demand. Connectors are used to electrically join the bus cable to the supply and service cables. A hundred or more such connectors might be installed when a manhole is built. Additional connectors might be needed later if power demands on the service network increase.
A typical supply bus in a manhole might include three 1500 KCM (thousand circular mill--indicating a diameter of around an inch and a half) cables, each connected to one of three electrical phases. A number of transformers supply power for each cable. Each of these supply cables might carry up to 600 amperes, with a phase-to-phase voltage of 208 or 460 volts. The three-phase power is available for air-conditioning, elevators, and other large loads. The typical supply bus also includes a ground cable, with the voltage between the ground cable and one of the other bus cables being 120 or 265 volts. This voltage is used for lighting, office equipment, etc. The supply and service cables might be 500 KCM (about one inch) in diameter.
While the service bus has been described above as being located in a manhole, because of increasing congestion in urban areas there is a growing tendency to install the supply bus for a low-voltage AC service network in the building which is to be served. A dedicated room called a "building vault" is used for this purpose. Building vaults are frequently positioned on top of buildings so that they will be near motors for air-conditioners and elevators. In a typical manhole both the supply cables and service cables extend downward from the bus cables. In a typical building vault, in contrast, the supply cables extend up to the bus cables and the service cables extend down to the bus cables.
A conventional double-tap connector may be bolted to a supply bus cable, and joined to the supply and service cables by compression indents, or crimps. Such conventional connectors protrude into the interior of the manhole or building vault, and thereby limit the space available for technicians to rack cables beneath the bus cables. Furthermore, the inventory requirements for conventional connectors are relatively high.